In recent years, as an energy conservation measure, the conventional type of pilot and main burner configuration for furnaces and similar equipment has undergone a significant change. For many years it has been conventional to provide a continuous standing pilot which provided a safety function by heating a thermocouple. The thermocouple provided a low power source of energy that had to be present before the main valve could be opened. This type of structure proved to be very safe and very inexpensive to install. The problem with this type of a pilot burner and safety system is that the pilot flame is present day in and day out, even through seasons of the year when the associated heating equipment either has no use or has very limited use. The rise in cost, and the need to conserve fuel has caused a change in the desirability of utilizing a standing pilot. In some states the standing pilot has been legislated out of existence, as an energy conservation measure.
Various approaches have been provided to replace a standing pilot with other types of equipment. One of the most common types of replacements for the standing pilot is a system that utilizes an ignition source such as a spark generator, and further utilizes a conventional flame rod to sense the presence or existence of the pilot flame. This type of system, even though substantially more expensive than a standing pilot, is now necessary in order to conserve gas. This type of a system allows for the ignition of the pilot immediately prior to the pilot actually lighting a main burner. Most of these systems rely on a flame rectification current passing through the pilot flame to verify its existence prior to opening the main valve for the burner. In theory, this type of a system is practical and safe. As a practical matter, however, this type of a system has certain limitations and deficiencies. By providing a flame sensor of the flame rectification type, the main valve of the burner was dependent on a signal that could vary in intensity and in some cases was marginal as far as safety was concerned. A conventional flame rectification system which operated the main valve of the burner was subject to unsafe failures due to fluctuations in the stability of the pilot flame, abnormalities in the ignition source, and in component failure in the electronics of the system.